This is a straightforward question, and the answer is not difficult either. We most commonly produce camera domes in thicknesses of 1.5mm, 3.0 mm, and 4.5 mm. They are used as follows:
The thinnest dome measures 1.5 mm (0.060 inches) at the flange. In acrylic this dome can be fairly brittle and therefore is only suitable for interior applications such as casinos, banks, retail and office environments where the dome is not going to be exposed to high winds, flying debris, or extreme vandalism. The primary advantage of this thinner dome is that the optical quality is superior, especially important for getting the absolute best image quality from your camera system.
The middle thickness of 3.0 mm (0.118 inch) is much more robust than 1.5 mm and is primarily used outdoors on weatherproof housings. Typical uses include: traffic camera housings, and camera housings for security systems around buildings and parking areas. Optical quality is excellent, well suited to the application.
4.5 mm domes are used much less commonly, but this thickness is available where extreme ruggedness is required. The optical quality is not as good as the thinner materials, resulting in less image resolution than can be achieved with 1.5 or 3.0 mm domes.
Custom domes can be produced in other thicknesses and other materials, so please check with us if your needs are not well satisfied by these three standard offerings.